1. Field of the Invention
The present invention relates to a synchronous circuit and a receiver for performing CDMA communication, which is one type of communication systems of a cellular phone, and the like, particularly to a synchronous circuit and a receiver which can determine a long code for use in communication in a short time, and receive signals.
2. Description of the Related Art
In the communication in which a code divisional multiple access (CDMA) system is employed, in order to reduce the influence of phasing, and meet the request for capacity enhancement, a specification called a wide band CDMA (W-CDMA) is proposed.
There are several codes for use in actual communication. In those codes, there are 512 codes for initial synchronizing in a base station, and the codes are divided into 16 groups. Specifically, 32 types of codes belong to each group.
Furthermore, a group short code indicating each group is allotted.
When power is supplied, a mobile station which performs the communication of the W-CDMA system captures a first perch channel to specify a base station with which the communication is performed.
As shown in FIG. 10(c), the first perch channel has an entire length of ten symbols, and is constituted of four pilot symbols, five logic channel symbols, and a first long code mask symbol with a length of one symbol. FIG. 10 is an explanatory view showing the signal formal of the W-CDMA system.
Additionally, the pilot symbols and logic channel symbols will generically be referred to as xe2x80x9cinformation symbolsxe2x80x9d hereinafter. The first long code mask symbol is diffused with an internationally unified short code.
Moreover, as shown in FIG. 10(d), a second perch channel is a channel for transmitting only a second long code mask symbol with a length of one symbol. The second long code mask symbol is diffused with specific one short code among the predetermined 16 types of group short codes.
Here, the first long code mask symbol and the second long code mask symbol are transmitted with the same phase.
Additionally, when the first perch channel is regarded as one unit (one slot time), 16 slot time units are referred to as a radio frame. The long code is repeated with the radio frame unit. Moreover, the unit of 64 radio frames is referred to as a super frame.
Here, the constitution for performing reception of a conventional mobile station will concretely be described.
A circuit (synchronous circuit) for capturing synchronization and receiving signals in the conventional mobile station is, as shown in FIG. 11, mainly constituted of a radio unit 1 for converting an incoming signal on an antenna to a base band signal; an A/D converter 2 for converting the signal inputted from the radio unit 1 into a digital signal; a spreading code generator 3 for generating a designated spreading code; a matched filter 4 for despreading the signal successively inputted from the A/D converter 2 with the spreading code inputted from the spreading code generator 3, and outputting a correlation signal; a profiler unit 5 for outputting a signal indicative of a signal incoming timing (path position timing) based on the correlation signal outputted from the matched filter 4; a plurality of correlators 6 for despreading the signal inputted from the A/D converter 2 with the spreading code inputted from the spreading code generator 3 over one symbol time from a plurality of path position timings inputted from the profiler unit 5, and outputting the correlation signals; a RAKE synthesizing unit 7 for RAKE-synthesizing the correlation signals outputted from the plurality of correlators 6; a decoder 8 for reproducing the original signal from the RAKE-synthesized signal; a voice CODEC 9 for converting the reproduced signal to a voice signal; and a controller 10 for controlling each unit. Additionally, the matched filter 4, profiler unit 5, and correlators 6 are collectively referred to as xe2x80x9cdespreading meansxe2x80x9d in the following description. FIG. 11 is a constitution block diagram of a conventional synchronous circuit.
Here, the matched filter 4 is, as shown in FIG. 12, basically constituted of a plurality of sample hold circuits 41, multipliers 42 disposed for the sample hold circuits 41, and an adder 43. FIG. 12 is a constitution block diagram of the matched filter in the conventional mobile station synchronous circuit.
Each component of the matched filter 4 shown in FIG. 12 will concretely be described. There are, for example, the number of chips per symbolxc3x97the number of over-samplings of sample hold circuits 41, which are connected to multiple stages. A first-stage sample hold circuit 41 holds the CDMA modulated signal inputted from the outside for a time of one chip time/the number of over-samplings, and outputs the signal to the next sample hold circuit 41.
Moreover, the subsequent sample hold circuit 41 similarly holds the signal inputted from the previous-stage sample hold circuit 41 for the time of one chip time/the number of over-samplings, and outputs the signal to the next sample hold circuit 41.
The multiplier 42 multiplies the signal held by the corresponding sample hold circuit 41, and the spreading code inputted from the outside, and transmits an output to the adder 43.
The adder 43 adds all the signals inputted from the multipliers 42 together, and transmits a correlation output to the outside.
Additionally, the operation performed by the multipliers 42 and the adder 43 will hereinafter be referred to as xe2x80x9cproduct sum operationxe2x80x9d.
Specifically, for the matched filter 4 in the conventional mobile station, a plurality of sample hold circuits 41 successively take the CDMA modulated input signals, and hold one symbol of information. The multipliers 42 multiply the separately inputted spreading codes and the signals held by the corresponding sample hold circuits 41, and the adder 43 adds multiplication results to output the correlation output.
When the controller 10 specifies, for example, the group short code based on the signal of the correlation output inputted from the matched filter 4, and obtains the long code for use in communication, a processing shown in FIG. 13 is performed. FIG. 13 is a flowchart showing the processing in the control unit 10 from when the group short code is specified until the long code is obtained.
As shown in FIG. 13, the controller 10 first detects whether it is synchronized with a slot (S1). When it is not synchronized (No), processing S1 is repeated, and is on standby until the synchronization is established.
Moreover, when the synchronization is established in the processing S1 (Yes), the group short code is successively set to the spreading code generator 3 (S2), and the spreading code generator 3 is allowed to generate the set group short code.
Subsequently, the controller 10 is on standby until the long code mask symbol is received (S3). When the long code mask symbol is received, the correlation output outputted from the matched filter 4 is checked, and it is judged whether or not correlation is obtained (S4).
Then, when no correlation is obtained (No), the processing returns to S2, thereby continuing.
Moreover, when the correlation is obtained in the processing S4 (Yes), the processing shifts to S5.
Subsequently, the controller 10 successively sets the code belonging to the group short code specified in the processing S2 to S4 to the spreading code generator 3 (S5), thereby allowing the spreading code generator 3 to output the code.
The controller 10 is on standby until the pilot symbol is received (S6), upon receiving the pilot symbol, checks the correlation output outputted by the matched filter 4, and judges whether the correlation is obtained (S7).
Subsequently, when the correlation is not obtained in the processing S7 (No), the processing returns to S5, thereby continuing. When the correlation is obtained (Yes), the long code indicated by the code having obtained the correlation is determined as the long code for use in communication.
Moreover, FIG. 11 shows a plurality of antennas, radio units 1, A/D converters 2, and despreading means, which means that the signals are received from a plurality of branches.
Furthermore, only a single correlator 6 is shown in each despreading means, but actually, each branch is provided with a plurality of correlators 6 in order that incoming signals passed through a plurality of paths are synthesized and RAKE synthesis is performed to enhance the reception signal intensity.
Since the RAKE synthesis is described in pages 143 and 144 of xe2x80x9cSpread Spectrum Communicationxe2x80x9d authored by Yukiji Yamauchi and published by Publication Bureau of Tokyo Denki University in 1994, the detailed description thereof is. omitted.
Furthermore, as not shown in FIG. 11 or 12, each matched filter 4 is in some cases provided with a register which temporarily holds the spreading code inputted from the spreading code generator 3.
The operation of the conventional mobile station synchronous circuit will next be described.
First, the receiving unit 1 receives the first perch channel from the incoming signal of the antenna, and the A/D converter 2 converts the signal to a digital signal.
Subsequently, the despreading means performs the despreading of the digital signal, and correlates/detects the first long code mask symbol. Since the signal format of the first perch channel has a length of ten symbols, it takes ten symbols at maximum until this correlation detection is obtained. A period in which a processing of correlating/detecting the first long code mask symbol is performed is hereinafter referred to as xe2x80x9cfirst phasexe2x80x9d.
When the first long code mask symbol can be correlated/detected from the first perch channel, the despreading means reverse-diffuses and correlates/detects the second long code mask symbol received with the same phase as that of the first long code mask symbol with each of 16 types of predetermined group short codes, and specifies the group short code. Time of 16 slots at maximum is required until this group short code can be specified. A period until the group short code is specified is hereinafter referred to as xe2x80x9csecond phasexe2x80x9d.
When the group short code can be specified, the despreading means successively reverse-diffuses the pilot symbol with 32 long codes belonging to the group indicated by the specified group short code.
Here, since each of 32 long codes has a length of 16 symbols ,the codes for diffusing one pilot symbol are codes which start from the 16 specific phases.
Specifically, since the despreading means needs to successively change 16 phases and calculate the correlation of 32 spreading codes and the pilot symbol, 32xc3x9716 =512 slot time is required. A period in which a processing of specifying the long code for use in communication is performed is hereinafter referred to as xe2x80x9cthird phasexe2x80x9d.
Since one slot time is 0.625 milliseconds, it takes 16xc3x970.625=10 milliseconds to specify the group short code, and it takes 512xc3x970.625=320 milliseconds to specify the long code for use in actual communication. Specifically, time of 10+320=330 milliseconds is required until the long code for use in communication is obtained.
The conventional receiver will next be described. Since the conventional receiver has the same constitution as that of the conventional synchronous circuit, it will be described with reference to FIG. 11.
As shown in FIG. 11, the conventional receiver is basically constituted of the radio unit 1, A/D converter 2, spreading code generator 3, two despreading means, and RAKE synthesizing unit 7.
Additionally, the despreading means is constituted of the matched filter 4, profiler unit 5, and the number of correlators 6 corresponding to the number of paths to be RAKE-synthesized.
Moreover, in order to receive the signals from two independent antennas for RAKE synthesis, there are two systems (two branches) of the radio unit 1, A/D converter 2, and two despreading means.
Additionally, since the operation of each component is the same as that of the above-described synchronous circuit, the description thereof is omitted.
The operation of the conventional receiver will next be described.
The radio unit 1 of each branch receives the incoming signal of the antenna, and outputs the signal to the A/D converter 2. The A/D converter 2 in turn converts the received signal to the digital signal and outputs the signal to the matched filter 4 and correlators 6.
On the other hand, the spreading code generator 3 generates the long code specified by the synchronous circuit, and transmits outputs to the matched filter 4 and correlators 6.
Subsequently, the matched filter 4 reverse-diffuses the digital signal inputted from the A/D converter 2 with the long code outputted by the spreading code generator 3 to generate a delay profile, and the profiler unit 5 detects and outputs a plurality of path position timings from the delay profile.
Then, the correlator 6 having received the input of the path position timing reverse-diffuses the digital signal inputted from the A/D converter 2 with the long code outputted by the spreading code generator 3 at the timing, and outputs the signal to the RAKE synthesizing unit 7.
Subsequently, the RAKE synthesizing unit 7 RAKE-synthesizes the signal to output demodulated data.
Here, the RAKE synthesizing unit 7 usually receives the input of reverse-diffused signal from each of two branches to perform the RAKE synthesis.
Additionally, the reason why each branch is provided with two despreading means is that when hand-over is performed moving between cells, the individual physical channel data need to be demodulated to establish synchronization with the signal of the base station as the addressee of the hand-over.
In the above-described conventional mobile station synchronous circuit, 330 milliseconds are required until the long code for use in communication with one base station is determined, which raises a problem that too much time is required until the communication can be started.
Furthermore, according to the specification, there is a restriction that three seconds or less should be taken until the communication can be performed. On the other hand, the long code for use in communication with eight adjacent base stations needs to be determined. Since this takes as much as about 2.6 seconds (330 millisecondsxc3x978), there arises a problem that even when the determination of the long code is unsuccessful, the long code cannot substantially be determined again.
Furthermore, since the conventional receiver is constituted by considering the hand-over or the RAKE synthesis, the circuit scale is enlarged, and the power consumption is disadvantageously increased.
An object of the present invention is to provide a synchronous circuit and a receiver in which a long code for use in communication can be determined in a short time, and circuit scale can be reduced.
According to the present invention, there is provided a synchronous circuit which performs correlating operation of a received signal and a spreading code to perform communication. When a long code is specified, a received long code mask symbol remains to be held over a given time, candidates for a plurality of spreading codes are successively selected, and correlation between the selected spreading code and the held long code mask symbol is successively calculated, so that the long code for use in communication can be determined in a short time.
Moreover, according to the present invention, in the synchronous circuit, the specifying of the long code as the spreading code for use in communication comprises remaining to hold a part of the signal diffused with the long code among the received signals over a given time, and changing a phase and successively calculating the correlation with the held pilot signal with respect to each of a plurality of long codes belonging to a group indicated by a group short code with the held pilot signal, so that the long code for use in communication can be determined in a short time.
Furthermore, according to the present invention, there is provided a synchronous circuit which comprises a radio unit for converting a signal coming in an antenna to a base band signal, an A/D converter for converting the signal inputted from the radio unit to a digital signal, a spreading code generator for generating a set spreading code, a matched filter for outputting a correlation signal from the digital signal inputted from the A/D converter and the spreading code inputted from the spreading code generator, and a control unit for controlling each unit. The matched filter comprises a plurality of sample hold circuits connected to multiple stages for successively transmitting data successively inputted from the A/D converter to a subsequent stage and storing the data, and for stopping the storage of newly inputted data, and continuing to hold the data held at the time while input of data stop signal is received from the control unit to stop the data storage; multipliers disposed for the sample hold circuits for performing multiplication with the corresponding spreading code inputted from the spreading code generator to transmit an output; and one adder for adding and outputting multiplication result signals inputted from the multipliers. Upon correlation/detection of a first long code mask symbol, at a timing when reception of a second long code mask symbol received with the same phase as that of the first long code mask symbol is completed, the control unit outputs the data stop signal to the matched filter, successively sets candidates for a plurality of group short codes to the spreading code generator, checks the correlation signals outputted by the matched filter with respect to the plurality of group short codes, determines that correlation is obtained, and stops the output of the data stop signal. At a timing when reception of a symbol diffused with the long code received with the phase immediately after the first long code mask symbol is completed, the control unit outputs the data stop signal to the matched filter successively sets a plurality of long codes belonging to the group indicated by the group short code to the spreading code generator with respect to each long code by changing the phase, checks the correlation signals outputted by the matched filter with respect to the plurality of long codes started from a plurality of phases, determines that the correlation is obtained, and specifies the long code having obtained the. correlation as the long code for use in communication, so that the long code for use in communication can be determined in a short time.
Furthermore, according to the present invention, there is provided a synchronous circuit which comprises a radio unit for converting a signal coming in an antenna to a base band signal, an A/D converter for converting the signal inputted from the radio unit to a digital signal, a spreading code generator for generating a set spreading code, a matched filter for outputting a correlation signal from the digital signal inputted from the A/D converter and the spreading code inputted from the spreading code generator, and a control unit for controlling each unit.
The matched filter comprises a memory for holding digital signal data inputted from the A/D converter over recent one symbol time, and continuing to hold the data held at the time while receiving the input of the data stop signal for stopping data taking from the control unit; and a product sum operator for performing product sum operation of the data stored in the memory and the spreading code inputted from the spreading code generator with the matched phase. Upon correlation/detection of a first long code mask symbol, at a timing when reception of a second long code mask symbol received with the same phase as that of the first long code mask symbol is completed, the control unit outputs the data stop signal to the matched filter, successively sets candidates for a plurality of group short codes to the spreading code generator, checks the correlation signals outputted by the matched filter with respect to the plurality of group short codes, determines that correlation is obtained, and stops the output of the data stop signal. At a timing when reception of a symbol diffused with the long code received with the phase immediately after the first long code mask symbol is completed, the control unit outputs the data stop signal to the matched filter, successively sets a plurality of long codes belonging to a group indicated by the group short code to the spreading code generator with respect to each long code by changing the phase, checks the correlation signals outputted by the matched filter with respect to the plurality of long codes started from a plurality of phases, determines that the correlation is obtained, and specifies the long code having obtained the correlationas the long code for use in communication, so that the long code for use in communication can be determined in a short time.
Moreover, according to the present invention, in the above-described synchronous circuit, when the spreading code for use is specified from the plurality of candidates, the control unit divides all the spreading codes as the candidates with a specific length, selects and synthesizes one spreading code from all the divided spreading codes, and sets the synthesized and obtained spreading code to the spreading code generator. The matched filter performs the product sum operation of digital signal data inputted from the A/D converter and the synthesized spreading code, calculates a partial correlation, and outputs the correlation signal, so that the long code for use in communication can be determined in a short time.
Furthermore, according to the present invention, in the above-described synchronous circuit, when the spreading code for use is specified from the plurality of candidates, the control unit divides the spreading codes as the candidates into a plurality of sets, divides all the spreading codes of each set into specific lengths, selects and synthesizes one a spreading code from the divided spreading codes, and sets the synthesized and obtained spreading code to the spreading code generator. The matched filter performs the product sum operation of the digital signal data inputted from the A/D converter and the synthesized spreading code, calculates a partial correlation, and outputs the correlation signal, so that the long code for use in communication can be determined in a short time.
Additionally, according to the present invention, there is provided a receiver which comprises: a plurality of data memories for detecting timings of a plurality of delayed incoming paths based on a received signal, and storing the signal received from the timing of each path as digital signal data; and means for despreading the data stored in each of the plurality of data memories in a time division manner. As the means, either one of a matched filter, a sliding correlator, and an inner product unit is selectively used, or all of them are used, so that the circuit scale is reduced, and the power consumption can be curtailed.
Moreover, according to the present invention, there is provided a receiver which comprises: a plurality of radio units provided with a plurality of antennas and disposed for the plurality of antennas for receiving signals coming in the antennas, and outputting base band signals; a plurality of A/D converters disposed for the radio units for converting the base band signals outputted from the corresponding radio units to digital signals; a spreading code generator for generating a spreading code; a plurality of profile means disposed for the A/D converters for despreading the received signals in accordance with the spreading code inputted from the spreading code generator to generate delay profiles, and holding the signals outputted by the A/D converters from timings of a plurality of path positions specified by the delay profiles; a change-over switch for selecting one profile means from the plurality of profile means; a control unit for changing the change-over switch at a certain interval in a time division manner in a given time; an inner product unit for successively performing product sum operation of the signals held by the profile means selected by the change-over switch and the spreading code inputted from the spreading code generator to transmit an output; and a RAKE synthesizing unit for RAKE-synthesizing the signals inputted from the inner product unit, so that the circuit scale is reduced, and the power consumption can be reduced.
Furthermore, according to the present invention, there is provided a synchronous circuit which comprises a radio unit for converting a signal coming in an antenna to a base band signal, an A/D converter for converting the signal inputted from the radio unit to a digital signal, a spreading code generator for generating a set spreading code, a matched filter for outputting a correlation signal from the digital signal inputted from the A/D converter and the spreading code inputted from the spreading code generator, and a control unit for controlling each unit. The matched filter comprises a plurality of sample hold circuits connected to multiple stages for successively transmitting data successively inputted from the A/D converter to a subsequent stage in a chip unit and storing the data; a switch for outputting the digital signal outputted by the A/D converter to the front-stage sample hold circuit among the sample hold circuits while receiving no input of data stop signal for stopping data taking from the control unit, and for outputting the digital signal outputted by the rearmost-stage sample hold circuit among the sample hold circuits to the front-stage sample hold circuit in the chip unit while receiving the input of data stop signal, to successively change the phase of the data stored in the sample hold circuit; multipliers disposed for the sample hold circuits for performing multiplication with the corresponding spreading code inputted from the spreading code generator; and one adder for adding and outputting multiplication result signals inputted from the multipliers. Upon correlation/detection of a first long code mask symbol, at a timing when reception of a second long code mask symbol received with the same phase as that of the first long code mask symbol is completed, the control unit outputs the data stop signal to the matched filter, successively sets candidates for a plurality of group short codes to the spreading code generator, checks the correlation signals outputted by the matched filter with respect to the plurality of group short codes, determines that correlation is obtained, and stops the output of the data stop signal. At a timing when reception of a pilot symbol received with the phase immediately after the first long code mask symbol is completed, the control unit outputs the data stop signal to the matched filter, successively sets a plurality of long codes belonging to a group indicated by the group short code to the spreading code generator, checks the correlation signals inputted from the matched filter with respect to the plurality of long codes for each phase of the pilot signal, determines that the correlation is obtained, and specifies the long code having obtained the correlation as the long code for use in communication, so that the long code for use in communication can be determined in a short time.